This invention relates to recording apparatus and more particularly to a drop height recorder which is adapted for shipment via a transportation system for recording such handling and environmental conditions as drop heights, drop impacts, shock events, temperature, relative humidity and the like.
An electronic recording accelerometer is known that is adapted to simulate a parcel which is sent through a parcel handling system such as the U.S. Postal System for recording shock, temperature, and relative humidity for a period of up to two weeks with the data being stored in semiconductor memories in two formats. One format is a statistical compilation of all valid events that occurred and the other is a time history of valid events that occurred. The exact magnitude of the event is not stored, but rather the event is classified into a number of predetermined amplitude levels or windows. For shock data, these windows are five G's wide from the base level of five G's to 80 G's and ten G's wide from eighty G's to 120 G's. The temperature windows are ten degrees F wide from -20 degrees F to +140 degrees F, and for relative humidity, the windows are ten percent wide from twenty percent to one hundred percent.
The known system uses three accelerometers for sensing acceleration along three mutually perpendicular axes; the accelerometers are connected to operational amplifiers and filters. The amplifiers raise the signal level sufficiently to be fed to the filters. The filters remove high frequency components of any shock wave sensed, as the low frequency components of the shock wave are of primary concern.
The three mutually perpendicular axes, temperature, and relative humidity analog signals are fed to encoding circuits which provide binary multi-bit data words of the levels sensed. The binary digital data words are applied to a statistical memory as well as respective time tagged memories for acceleration, temperature, and relative humidity. The statistical memory provides a count of the various levels of acceleration, temperature and relative humidity sensing while the time tagged memories provide stored time dependent data of the maximum values sensed during selectable time periods within the time allotted to send the apparatus from one destination to another. Those persons skilled in the art desiring more information for the known apparatus are referred to U.S. Pat. No. 4,114,450 issued Sept. 19, 1979.
The essential difference between the known apparatus and the present invention is that the present invention stores amplified signals of a triaxial accelerometer during free-fall (also referred to hereinafter as "zero G" signals) as pre-trigger event data, plus the full waveform of post-trigger acceleration signals in a solid state memory. The drop heights are determined from the data recorded prior to drop impact, from which the time spent in free-fall (zero G) can be ascertained and used to calculate the drop heights. The post-trigger, full waveform acceleration signals enable the packaging engineer to duplicate the impact accelerations in the laboratory on shock testing apparatus for testing improved packaging designs.